When timber is harvested and hewn into lumber, it is considered green, that is, the lumber has not been conditioned and has a high internal moisture content. Green wood is often not desirable for use in many applications as the lumber will tend to shrink as it dries, creating gaps or voids when used in construction of structures or objects. Additionally, as the lumber dries, it can warp, split, or crack which can weaken or damage the structure or object created using the green wood. Further, for some applications, the high moisture content of the wood can prevent its use as necessary or desired processes cannot be performed on wood having a high internal moisture content.
To avoid these potentially negative drawbacks, the wood can be seasoned, allowing internal moisture of the wood to evaporate to a desired or sufficient level for use of the wood or lumber in a desired application. A typical method of seasoning wood is to leave the cut lumber outdoors, exposed to the elements, allowing the internal moisture content of the lumber to equalize with the local environment. Once equalized, the lumber will likely not change dimensionally when used in an application, i.e., the lumber will not warp or contract. To achieve this seasoning, the wood or lumber must often be left to season for an extended period ranging from months to years. As such, a large area is needed to store the lumber as it seasons and a seller will have to wait the seasoning time before selling the lumber.
To speed the process of seasoning, the lumber can be placed in a kiln to dry the lumber to the desired internal moisture content more rapidly. Lumber is placed within the kiln and heated to evaporate the internal moisture, seasoning the wood in a fraction of the time required for passively seasoning the wood or lumber outdoors. Kiln drying lumber can increase the cost of the final product as more economic investment is required to purchase and operate the necessary equipment. However, the reduced time to season the lumber and the control over the final moisture content of the lumber can have economic benefits that justify the increased costs to produce the final lumber product.
A typical kiln can be an enclosed unit in which the lumber is placed and a desired process or cycle of heating and cooling the lumber is carried out within. However, the process, while shorter than seasoning outdoors, can take days or months, which can limit the amount of lumber that can be processed through the kiln.
It would be desirable within the industry to have a continuous kiln able to process and dry large volumes of lumber. Additionally, it would be desirable for the kiln unit to be compact and efficient.